This invention relates to electron beam tubes. Particularly, but not exclusively to linear electron beam tubes, as used for example, in broadcast transmitters for amplifying RF signals for transmission.
A number of types of linear electron beam tubes are known for RF signal amplification. These types include klystrons and Inductive Output Tubes (IOT's) as well as travelling wave tubes. Traditionally klystrons have been used to amplify RF signals for broadcast. However, klystrons are relatively inefficient amplifiers and are very expensive to run. In recent years, IOTs have replaced klystrons as they are inherently more efficient and so reduce operating costs. More recently, an improved efficiency version of the IOT has been developed: the ESCIOT (Energy Saving Collector Inductive Output Tube) which uses a multi-stage depressed collector.
It is desirable for an electron beam tube in a transmitter to be able to broadcast both digital and analog television signals. A few years ago it was considered that analog signal transmitters would be phased out by 2006. However, it is now clear that this will not be the case. Analog signals require more power than their digital counterparts and there is, therefore, a need to improve the efficiency of devices designed with digital transmission in mind, and to minimize heat losses that occur within the device which will be more problematic at higher operating powers. As well as the requirement for Analog and Digital compatibility there is a general need to increase the efficiency of linear beam tubes to reduce operating costs.
Linear beam tubes are also used in other fields, for example in scientific applications such as synchrotrons, driving superconducting cavities and accelerators.